1. Field of the Invention
The present invention relates to a shroud and a rotary vane wheel of a propeller fan and the propeller fan.
2. Description of the Related Art
A vehicle is provided with a propeller fan for cooling heat exchangers such as a radiator and a condenser of an air conditioner. Japanese Patent Application Laid-Open No. 2002-47937 discloses a stay for supporting a boss of the fan to a shroud. To achieve high fan efficiency and low noise when running at low speed, this stay is of an aspect ratio >1, has a longitudinal direction of its section oriented toward a direction of an airflow generated by driving the fan and also has a cavity provided on a side of a negative pressure of the stay generated by the airflow when the vehicle is running at high speed.
An engine room of the vehicle hardly has space because it has not only an engine as a power source of the vehicle but also its accessories mounted therein. For this reason, the propeller fan for cooling the radiator and condenser is limited as to its dimension in the airflow direction. Consequently, the space between the fan and the stay becomes small, and noise when operating the propeller fan becomes high. The stay is required to have strength for supporting the fan and driving means (an electric motor for instance) of the fan. This strength cannot be secured, however, if the stay is rendered thin in an attempt to reduce the noise when operating the propeller fan. Such a problem is not considered in Japanese Patent Application Laid-Open No. 2002-47937. Therefore, there is room for improvement in a conventional technology disclosed in Japanese Patent Application Laid-Open No. 2002-47937 as to reducing the noise while limiting the dimension in the airflow direction and further securing support strength of the stay (first problem).
As for the propeller fan for cooling the radiator and condenser for the vehicle, it is placed in a narrow engine room and required to be further lightweight, and so there is a strong request for compactification regarding a depth dimension in a flow direction of cooling wind. If the depth dimension is thus reduced, however, a cross-section of a cooling wind channel of the shroud of the propeller fan changes drastically because the radiator on an upstream side is rectangular while an air sucking path of the propeller fan is round. For this reason, there is a problem that an uneven drift is formed in a circumferential direction of the propeller fan (rotary vane wheel) to generate unpleasant BPF (Blade Passing Frequency) noise.
The radiator and condenser as cooling subjects are small-size and require high heat exchange performance so that ventilation resistance thereof is high. For this reason, the propeller fan is driven under a condition of a high static pressure difference reverse to an adverse wind direction. In this case, there is a problem that the flow on a propeller plane of the rotary vane wheel breaks away so as to increase input and the noise under the same air volume condition.
As for these problems, there is a known technology described in Japanese Patent Application Laid-Open No. 7-167095 regarding a conventional propeller fan. The conventional propeller fan (electric fan) is the electric fan rotatively driven by the electric motor, which comprises a boss portion for rotating by receiving a driving force of the electric motor and 9 to 13 blades (blade portion) placed around the boss portion circumferentially apart from the boss portion. The blade is characterized by being a forward swept vane of which angle of advance overlooking a vane edge from a vane root is 35 to 45 degrees.
However, the propeller fan described in Japanese Patent Application Laid-Open No. 7-167095 is not sufficient as to noise reduction performance (second problem).
As the rotary vane wheel provided to the conventional propeller fan has multiple blades in general, the multiple blades rotate on rotating the rotary vane wheel by the driving means such as the electric motor so as to let the air flow by means of these blades. Thus, these blades for blowing air by letting the air flow are fixed on a hub of the rotary vane wheel. The hub is provided to connect the blades to an axis of the driving means and transfer rotation of the axis of the driving means to the blades. For that reason, the hub does not contribute to air blowing so much. Therefore, there is a conventional rotary vane wheel wherein occupancy of the blades in the rotary vane wheel is enlarged to increase a sent air volume so as to improve air blowing performance. In Japanese Patent Application Laid-Open No. 2004-218513 for instance, a joint of the blades and the hub is extended inward in a radial direction centering on a rotation axis of the hub to increase length of the blades in the radial direction. It is thereby possible to improve the occupancy of the blades in the case of axially viewing the rotary vane wheel so as to increase the sent air volume and improve the air blowing performance.
In the case of the above-mentioned rotary vane wheel, however, there is little difference in that the hub does not contribute to improvement in the air blowing performance so much because the hub is basically in a cylindrical shape. As with the above-mentioned rotary vane wheel, the blades are extended inward in the radial direction centering on a rotation axis of the hub so that a radial step is generated on an end of the upstream side of the hub in the circumferential direction of the rotation axis. Therefore, there is a possibility that the airflow may be disturbed in this part. In the case where the airflow is thus disturbed, the efficiency lowers and so there is a possibility that the air blowing performance may lower and the noise may be easily generated (third problem).